在 iPad 上使用 JS 进行图像缓存

我正在开发一个用于iPad的纹理选择器。所以基本上只是一堆图像元素。为了避免图像重新加载和滞后，我在 JS 中缓存并重用Image对象。有点像这个

/**
 * Asynchronous version of memoize for use with callback functions. Asserts
 * that last argument is the callback.
 *
 * @param  {Function} func
 * @return {Function}
 */
 util.memoize.async = function(func) {
    var cache = {};
    return function() {
        var hash = JSON.stringify(arguments);
        var args = Array.prototype.splice.call(arguments, 0);
        var callback = args.pop();
        if (hash in cache) {
            return callback.apply(this, cache[hash]);
        }
        args.push(function() {
            cache[hash] = Array.prototype.splice.call(arguments, 0);
            callback.apply(this, cache[hash]);
        });
        return func.apply(this, args);
    };
};
/**
 * Creates new Image element and calls back with loaded image.
 * @param {string} url
 */
io.GetImage = function(url, callback) {
    var img = new Image();
    img.onload = function() {
        callback(img);
    };
    img.src = url;
};
picker.image_ = util.memoize.async(io.GetImage);

然后，每当我需要图像时，我都会调用picker.image_并获取缓存的图像。它在桌面，Chrome，Firefox，Safari上完美运行，但在iPad上，我得到了空的（未加载的）图像。为什么？我真的很喜欢这种方法，它的表现非常好。

看起来好像移动野生动物园从DOM中删除图像数据时会丢弃图像数据。可能是这样吗？

更新：澄清一下，正在加载的数据是动态的，因此它不是AppCache的最佳用例。

更新*：没有完全令人满意的答案，这是我的解决方案。请注意，复制方法非常慢。

/**
 * Creates new Image element and calls back with loaded image.
 * @param {string} url
 */
var GetImage = function(url, callback) {
    var img = new Image();
    img.onload = function() {
        callback(img);
    };
    img.src = url;
};
/**
 * @param {number} num maximum number of stored images
 */
var ImagePool = function(num) {
    this.limit_ = num;
    this.canvases_ = {};
    this.order_ = [];
};
/**
 * Retrieve image from cache.
 *
 * @param  {string}   url      URL of request image
 * @param  {function(HTMLCanvasElement)} callback
 */
ImagePool.prototype.get = function(url, callback) {
    if (this.canvases_[url] !== undefined) {
        callback(this.copy_(url));
    } else {
        if (this.limit_ && this.order_.length == this.limit_) {
            delete this.canvases_[url];
            this.order_.pop();
        }
        GetImage(realUrl, function(img) {
            var c = document.createElement('canvas');
            c.width = img.width;
            c.height = img.height;
            var ctx = c.getContext('2d');
            ctx.drawImage(img, 0, 0);
            this.canvases_[url] = c;
            this.order_.unshift(url);
            callback(this.copy_(url));
        }.bind(this));
    }
};
/**
 * @param  {string} url
 * @return {HTMLCanvasElement}
 * @private
 */
ImagePool.prototype.copy_ = function(url) {
    var c = document.createElement('canvas'),
        cached = this.canvases_[url];
    c.width = cached.width;
    c.height = cached.height;
    var ctx = c.getContext('2d');
    ctx.drawImage(cached, 0, 0);
    return c;
};